Liquid level gauge



Feb. 7, 1950 s. L. ADELsoN LIQUID LEVEL GAUGE 5 Sheets-Sheet 1 Filed Oct. 25, 1946 w w w w Feb. 7, 1950 s. L. ADELsoN LIQUID LEVEL GAUGE 5 Sheets-Sheet 2 Filed Oct. 25, 1946 INVENTOR.

Feb. 7, 1950 s. L. ADELsoN 2396365 LIQUID LEVEL GAUGE Filed OGt. 25, 1946 5 Sheets-Sheet 3 Feb. 7, 1950 s. L. ADELON LIQUID LEVEL GAUGE 5 Sheets-Sheet 4 Filed Oct. 25, 1946 Patented Feb. 7, 1950 w LIQUID LEVEL GAUGE Samuel L. Adelson, Chicago, Ill., asslgnox' to Iniilco Incorporated, Chicago, Ill., a corporatlon of Delaware Application amber 25, 1948, serial No. 705,577

Claims.

This invention refers to a telemetric device adapted to detect very small motion of movable members and to'telemeter the magnitude of such motion to a remote point, and is particularly adapted to measure and transmit variations in the level of a liquid.

A primary object of this invention is to provide an improved liquid level measuring device.

z -Another principal object of this invention is to provides. device which detects very small changes in the'elevation of a watersurface (accurately registers variations of approximately 1/1000 of an inch when using the fioat shown in Figure 1, and approximately 15/1000 of an inch when using the whisker shown in Figure 5) and accurately transmits such changes to a remotely located receiver, which may indicate or record the changes, as well as the elevation of the water level at any particular time.

Still another object of this invention is to provide an apparatus for measuring the level of a liquid, the apparatus utilizing a single contact which directly or indirectly contacts the liquid surface and which is automatically raised or lowered so as to follow the liquid surface, as distinguished from meters of -this type which utilize a plurality of fixed contacts, each of which is connected to a resistance of different value.

A further object of my invention is .to provide a liquid level meter, or gauge, particularly adapted for telemetering systems, which is of simple construction and which is accurate over an infinite range of values.

These and other objects will be apparent, from the description and claims which follow.

One of the elements of the meter, or transmitter, of my invention is known commercially under the trade name UFlashtron" which is an electronic device providing two immediately responsive, inertialess relays. A detail description of a "Flashtron is found in Patent No. 2,208,235 of July 16, 1940. An element of the Flashtron is an actuator circuit which. when closed externally (even through a resistance as large as 20,000 ohms) will render only one of the relays conductive, while if the actuator circuit is broken only the other of the relays will be rendered conductive, whereby one or the other of the relays is always conductive depending upon whether the actuator circuit is opened or closed. In those cases in which extreme accuracy is not necessary, one of the relays can control the fiow of current through one of the coil circuits of a reversible motor while the other relay controls the fiow of current through the other of the coil circuits, so that the motor will rotate in one direction or the Vother dependlng upon whether the actuator circuit is opened or closed. However, I prefer, in order to secure extreme accuracy, to use two unidirectional motors in opposed relationship, one

of the motors being connected to a source of power through one of the F'lashtron relays and the other motor connected through the other. The two motors are connected to a diiferential gear arrangement whereby a gear cage will rotate in one direction or the other depending upon which motor is motionless or running at a speed lesser than that of the other, but which will remain motioniess when both motors rotate at the same speed. Another element of the meter is a single contact member, directly or indirectly contacting the liquid level to be measured, which is connected to the reversible motor or the gear cuit is opened or closed. By placing the contact and the liquid whose level is to be measured in the actuator circuit it is obvious that the contact member can be made to rise if it is in contact with the liquid and to lower if it is not. Still another tion and of the drawings which form a part thereof and in which:

Figure 1 represents a side view, partly in cross section, of one embodiment of my invention in which the transmitting element comprises a Wheatstone bridge circuit.

Figure 2 is an enlarged detail of the differential gear arrangement and cage using the two opposed unidirectional motors to position the contact 'and the transmitter.

Figure 3 is an end view of the gear cage shown in Figura 2 taken along the plane indicated by line 3-3 of Figure 2, showing one method of positioning both the contact and the transmitter from movement of the differential gear cage.

Figure 4 is a diagrammatic wiring sketch of the complete Wheatstone bridge circuit associated with the embodiment shown in Fgure 1.

Figure 5 is a side view, partly in cross section, of another embodiment of my invention which utilizes a very sensitive Selsyn motor as the electric transmitter.

Figure 6 is a top view of the apparatus shown in Figure 5.

Figure 7 is a schematic wiring diagram of the complete power circuit of my apparatus, utilizing, for purposes of illustration, the telemetering apparatus of Figures 1 and 4.

The apparatus of my invention is mounted on a suitable supporting plate |0- which is preferably supported at a desired elevation by a standard and base lla resting on the floor I 2. It will be reco-gnized that for delicate and accurate measurements the apparatus should be level so aaaasee i .3 that in my preferred form the base plate ||a is provided with leveling acrews |3 threaded into base plate ||a and locked in position by lock nuts |4.` A guide tube il, preferably of metal, depends from the supporting plate |0. A metal rod |6 is slideably mounted in the guide tube ll and carries the non-conducting guides |1, as shown. The diameter of the guides |1 is slightly less than the inside diameter of guide tube |6 so that rod |6 is free to slide within the guide tube |5 substantially in the center thereof. Also,

it will be obvious to those skilled in the art that the rod |6 can dip directly into the liquid in the pot or chamber |0, as is shown in Figure 5, but I have found that much more accurate measurements can be secured by utilizing a fioat supported contact such as shown in Figure 1. As indicated above. the fioat contact provides accurate measurements of variations as small as approximately .001", while the direct contact is accurate only to approximately .015", due to the action of the surface film on the water when direct contact is used. The rod |6 is connected by an insulator 20 to a chain which is raised or lowered by the reversing device to be described hereafter. Below the lower end of the guide tube is a fioat pot or chamber |8, preferably of metal, which is connected to the liquid whose level is to be measured by means of pipe |0. It is preferred that the pot |0 be of such depth as to cover the entire range of the depth of liquid to be measured, as it is desired to use the pot or basin |0 as one arm of a U tube, the other arm being the body of liquid whose surface is to be measured. It will be obvious, of course, that the rod |6 can dip directly into the body of liquid, the surface of which is to be measured, but for most purposes it' is more satisfactory to provide the small chamber |6 directly connected to the liquid.

In the embodiment shown in Figure 1 a yoke plate 30 is attached to the lower end of the metallic rod l6. A pair of legs 3| depend from the yoke plate 30 and carry a contact plate 32. On the upper surface of the contact plate 32 is a contact point 33. A float 34 rides on the liquid in the fioat chamber |0. Preferably the float is of substantially the same size as the float chamber |8 so as to prevent tilting in the liquid. Rising from the iloat 34 are standards 35 which carry a contact plate 36 and an insulating plate 31. The contact plate 36 is always in contact with standards 35. As shown in the drawing the legs 3| pass through corresponding holes in the contact plate 36 and the insulating plate 31. The holes 38 in the contact plate 36 are relatively large while the guide holes 30 in ,the insulating plate are just large enough to permit free passage of the legs 3| and thereby provide guides for the legs. It is necessary that there be no possible chance of electrical contact between the legs 3| and the contact plate 36, for

closing of the actuator circuit must come through contact between the contact point 33 and the contact plate 36. In other words, in order to achieve accuracy, the actuator circuit must be opened and closed only ;between the contact point 33 and the contact plate 36. The legs 3| and wardly will not be impeded at any time, nor will the downward movement of the rod Il be imp`eded at any time, regardless of the rate at which the float may move upward ,or the rate at which the rod may move downward.

Also mounted on the supporting plate |0 is a "Flashtron" which includes two similar electronic tubes 4| and 42. As pointed out above, a Flashtron" is an electronic device which can be purchased on the open .market and, therefore, need not be described in detail. Essentially, a Flashtron constitutes a'pair of immediately responsive and inertialess relays. One of the relays is operative upon closing of the actuator circuit while the other is operative upon the opening of the actuator circuit. Thus one or the other of the relays is open at all times.

The power supply for the apparatus may be of any suitable characteristic although I have preferred to use a 110 volt, cycle current, as that is the type most usually available. As shown in Figures 1 and 7, the power lines L1 and La lead to binding posts 43 and 44, respectively, and thence through conductors 45 and 46 to the power input binding posts 41 and 46 of the Flashtron. The Flashtron is also provided with binding posts 48 and 50 for the actuator circuit and binding posts 5|, 52 and 53 for connection to the reversible device to be operated.

The actuator circuit may comprise a ground Wire 60 connecting the binding post 49 to the metallic guide tube |5. The tube |5 is connected to the iloat Chamber or pot |6 by means of conductor 6|. A conductor 62 leads from the other actuator binding post 50 to another binding post 63, from which leads a ilexible wire 64 connected to the rod 6. The actuator circuit thus leads from the Flashtron binding post 50, through conductor 62, binding post 63, flexible wire 64, rod |6, plate 30, legs 3|, plate 32, contact point 33, contact plate 36, risers 35, fioat 34, to the liquid in the float chamber |0, thence to the walls of the iloat chamber |8, conductor 6|, guide tube |5 and conductor 60 to the binding post 46. Thus the actuator circuit is closed when the conact point 33, carried by the rod |6, engages the contact plate 36, carried by the-iloat 34, and is opened when the two'are apart. The actuator circuitv is opened and closed only between the contact point 33 and the contact plate 36, and a separation of the order of 1/nma of an inch between the two is sufiicient to open the actuator circuit. The actuator circuit thus is closed immediately the two are in contact, even though the resistance of this circuit is as large as 20,000 ohms.

A reversing device operated by the Flashtron" is used to raise and lower the contact rod |6. This might be a reversible motor if accuracy and delicacy are not important. However, I prefer to use two unidirectional motors in opposed relationship and connected to a differential gear system, as I have found that they are much more delicate and accurate. Flgure 2 shows a prethe standards, or risers, 36 are so proportioned double arm 11 having a hub 18 is rotatably mounted on the shaft 13 between the motor 1| and bevel gear 15. A pulley 19 having a hub 80 is rotatably mounted on shaft 1| between lthe motor 12 and its bevel gear 18. Cross pieces 8| and 82 having bosses`83 and 84, respectively, have one end bolted to the double arm 11 and the other end bolted to the pulley 19, as shown. A shaft 85 is journaled in the bosses 83 and 8|. Two bevel gears 86 and 81 are rotatably mounted on the shaft 85, their hubs preferably being backed against the respective bosses of the cross pieces and separated, one from the other, by a spacer 88. These two last mentioned gears 88 and 81 are so arranged that they are meshing with bevel gears 15 and 16. The driving gears 15 and 16 and the driven gears 86 and 81 form a differential gear system, and the double arm 11, pulley 19 and cross pieces 8| and 82 form a gear cage for that system. It is obvious that if the two drlving gears rotate at the same speed (and in opposite directions) then the gear cage will remain stationary, but if one of the driving gears is rotated while the other is either stopped or rotated at a lesser speed then the cage will rotate in one direction or the other.

A second pulley 89 of suitable diameter is rigidly secured to the pulley 19, as shown in Figure 3. A chain 90 is secured at its upper end to the sec'- ond pulley 89 and at its lower end, as shown in Figure l, engages a hook carried by the rod insulator 20. A second chain 9| is fixed at its lower end to the pulley 19 (shown in Figure 3) in such a manner that the second chain is unwound as the first chain is wound up. The second chain 9| passes over pulleys 92 and 93 and has a counterweight 94 attached to its free end. This second chain 9| is used to position the transmitting device.

' The output circuits of the "Flashtron" are connected to the two motors so that one motor is operated when the actuator circuit is closed and the other is operated when the actuator circuit is open. As best shown in Figure 7, the conductor leads from the binding post 52 to both motors 1| and 12. A second conductor |00 leads from binding post to the motor 1| and a third conductor |02 leads from the binding post 53 to motor 12.

A telemetric transmitter is operated by movement of the second chain 9|. This sender may comprise a Wheatstone bridge arrangement, shown in Figures 1 and '1, or a Sensitive Selsyn motor as shown in Figures 5 and 6. Both types operate satisfactorily and other means 'may be suggested by those skilled in the art. In the embodiment shown in Figure 1 a carriage ||0 is attached to the chain 9|, as by hooks and ||2. The carriage ||0 rides on a rail ||3. Fixed to the carriage is a bridge contact H, which bridge is spaced between a uniformly and finely wound resistance coil |5 and a. return rod |6. The resistor ||5 is one arm of a Wheatstone bridge circuit hereinafter described in connection with Figures 4 and 7. The resistance of this arm of the Wheatstone bridge will depend upon the position of the carriage ||0, the resistance increasing as the carriage .moves toward the right. As best shown in Figure 7, the binding posts |1, ||8 and ||9 are connected to the resistance coil in the usual manner and also to binding postsV |23, |24 and |25 by means of conductors |20, |2| and |22, respectively. The binding -posts |23, |2| and |25 are adapted to receive the wires (shown as 6 dotted' lines in Figure 4) for connection to the receiving instrument.

The telemetering arrangement is shown in Figures 4 and 7 in which the receiver is indicated generally at |30. Such a receiver is adapted to indicate or record, or both, a magnitude which is proportional to the value of a remotely located resistance, such as ||5 in Figure 1. There are several well known commercial devices on the market so that the receiver need not be described in detail. Briefly, such a receiver usually includes a Wheatstone bridge circuit including the equal resistance arms R and R and a third arm including the group of resistance R1 and R2 and ||5a of which the latter only is variable. At the transmitting station is located the fourth arm of the Wheatstone bridge which is a com-' bination of the resistance R1, Rz and ||5 which are equal to R1, Rz and ||5a, respectively, of the receiver |30 (the resistance ||5 being variable as is the resistance ||5a) The transmitter and the receiver are connected by conductors 3|, |32 and |33 as shown. Thus any change in the value of the resistance |5 at the transmitter caused by a change of the liquid level in the fioat chamber |8 is therefore automatically indicated or recorded at the receiver |39.

When contact 33 and plate 36 are in contact one of the motors, as for example, motor 1|, will rotate in a direction which will lower rod IG and open the actuator circuit, When contact point 33 and contact plate 36 are separated the other motor, for example, motor 12, will rotate in a direction which will raise the rod IB to again make contact with the plate 36. If we assume the level of the liquid in the stream is stationary then the level of liquid in the float chamber |8, as well as the float 34, will also be stationary. Assuming further that at a certain instant, contact 33 engages plate 36, then the actuator circuit will be closed and immediate operation of motor 1| at a higher speed than the motor 12 (the circuit to which is broken but which will, through inertia, rotate at a decreasing Velocity), will cause the gear Cage to rotate in a direction to lower the rod 6 and thus break the actuator circuit. Instantly, the circuit is broken, motor 12 will operate at a greater speed than motor 1 |J and rotate the gear cage to raise the contact 33 to again make contact with plate 39 and close the circuit, whereupon the cycle will again be repeated. It is evident that if the motors 1| and 12 were rotating at the'same time the gear cage or frame would remain stationary and pulleys 19 and 89 would not move. On the other hand, if

motor 12 rotates and at the same time motor 1| w does not rotate, then the gear frame will move in a clockwise direction (when viewed as shown in Figure 3) and chains 90 and 9| will move in an upward direction. Conversely, if motor 1| rotates and at the same time motor 12 does not rotate the gear cage will move in a reverse direction and chains and 9| will move in a downvwill be applied alternately to motor 1| and 12 at extremely short intervals. However, because 7. of the inertia of their respective rotors, they will slow down slightly when power is removed, but will not stop. For example, when, because of the rapidly alternately opening and closing of the actuator circuit between contact 33 and plate 33. these contacts separate momentarily power will be removed from motor 1|. Because of the inertia of its rotor the motor 1| will continue to rotate at a decelerated velocity as power is applied to motor 12. At the instant power is removed from motor 1| it is applied to motor 12 and that motor will be accelerated, and the gear cage will be movedslightly to again secure contact between the contact point 33 and plate 33. Also, during the momentary contacting of contact 33 and contact plate 3G, power will be removed from motor 12, but, because of the inertia of its rotor, it will continue to rotate, thereby tending to maintain the gear cage stationary. This tendency is immediately neutralized by the acceleration of motor 1| to which power is applied the instant power is removed from the motor 13. The use of two simple motors and the differential system, together with the other elements associated therewith, results in no perceptible movement of the cage HO and therefore no change in the resistance of Wheatstone bridge arm H! when there is no change in the level of the liquid in the float chamber |8.

Thus oscillation of contact 33 over a very small amplitude (which may be about 1/1000 of an inch or slightly more) will continue so long as the level of liquid does not change. Correspondingly, the relative velocities of the motors will oscillate at the same rate, so that their associated difierential gearing and gear cage, including pulleys 19 and 39 will oscillate at relatively high frequency. However, such oscillation is over such small amplitude and at such frequent intervals that in eflect the pulleys 18 and 13 do not move, the carriage IIII does not move and the resistance of arm 5| does not change.

Should the level of liquid rise, then the float will rise and contact plate 36 will be raised away from contact point 33 to open the actuator circuit. This causes motor 12 to raise the rod IGv and contact 33 toward the new position of plate 38 and when contact is secured oscillation proceeds as previously described. Until a position corresponding to the new level has been reached. the motor 1| will have been inoperative and motor 12 will, therefore. rotate the gear cage to the new position and will also have caused carriage ilfl to travel towards the right to a position corresponding to the new float level and the resistance HS of the Wheatstone bridge circuit will assume a higher value corresponding to the higher level of the liquid.

On the other hand, should the level of liquid fall the float 3| will remain suspended upon contact point 33. So long as contact '33 is in contact which plate 36 the motor 12 will be inop-A erative while the motor 1| will rotate the gear cage to both lower the rod and contact 33 and also to move the carriage I Ill to the left to lower the resistance of resistance coil IIS. When the float 3| again freely boats upon the surface of the liquid oscillation will again proceed as previously described.

The embodiment shown in Figures 5 and 6 is essentially the same as that shown in the preceding figures differing therefrom only in slight particulars. One of the principal diiferences is that the contact point is a whisker which directly contacts the water, or other liquid, the levelv nas 8 of which is being measured. Another diflerenee is that the contact is raised and lowered by gear- -ing instead of a chain. A third difference lies in the fact that the differential gear frame drives a Selsyn motor instead of positioning a contact on a resistance. In such a system the receiving instrument is another Selsyn motor which, if it is desired to perform work, may be connected to an amplifler.

In this embodiment the base plate lila is supported by a standard ll. Mounted on the bo!!! plate Ia is a pair of opposed unidirectional motors 1| and 12, associated with which is a gear system and a gear frame. or cage, such as descrlbed in connection with previous figures. 'The entire assembly of motors. gears and gear frame is identical with that described in connection with Figure 2 except that a gear I" is substituted fo'r pulleys 1| and 39. Meshing with the gear Ill is an intermediate gear III which is keyed to a shaft I!! which in turn is journaled in bearing |53. A Selsyn motor i" is also mounted on the base Ina and is driven by a gear I which meshes with the intermediate gear IH. Thus, rotation of the gear cage positions the Selsyn motor Ill. The use of a Selsyn motor as a telemetering instrument is well known in the` art and need not be described. Suflice to say that it is connected in the usual manner, with wiring, not shown, to a similar Selsyn motor in the receiving instrument, and, due to the characteristics of such motors, the receiving motor will assume the same position as that of the motor in the transmitter. Modern Selsyn motors of high efllciency give a highly delicate measurement over an inflni range of magnitude without logging between the two motors. Thus the motor of the receiving instrument gives a reading corresponding to that of the transmitting motor with an accuracy corresponding to about 1/1000 of an inch in the liquid level being measured.

Extending horizontally from a bracket Ill, on the base plate Na, is a tubular arm I 3|. The outcr end of the arm 13| provides a bearing i" in which is Journaled a shaft |l3 that extends along the center axis of the arm IGI. The transmission shaft |63 is coupled to the shaft I!! by any suitable coupling means, such as the bellows I". A gear ISS is keyed to the transmission shaft i63 as shown.

The guide tube |5a is mounted on the arm IBI by any suitable means such as by welding. The contact rod Ifa provides a rack I which meshes with the gear I", so that rotation of the shaft |S3 will raise or lower the contact rod lla.

For purposes of Illustration I show a contact whisker |1I fixed to the lower end of the contact rod la, the whisker directly engaging the liquid in the pot ia. As indicated above, the float contact described above in connection with Figure is far more accurate than direct contact of the 'whisker with the liquid. However, for many pur- ,including it. It should sufiice to say that the actuator circuit is connected through the basin Ila and the whisker |1I` to supply power to one motor and to cut off power to the other motor.

While in this description the application of this invention was described with particular reference to indicating or` recording the surface level and changes, minute or great, in the surface level of a liquid, it will be evident to those skilled in the art that the invention may be applied to indicate, or record, positions and changes in position of any movable member. Further, it will be evident to those skilled in the art that the same mechanism which automatically positions the mechanism at the receiver may also be used to perform work as well as to position a pointer. Thus, the receiving mechanism may not only indicate or record the changes in the magnitude, but may also do some work in connection therewith, such as controlling the feeding of adosing chemical to a water supply or the like. It will also be obvious to those skilled in the art that it will be desirable to provide limit switches to prevent appreciable overtravel of the motors beyond their Operating limits, but as such things are well known they have been omitted from the drawings and description in order to simplify understanding of my invention.

I claim:

1. Apparatus for measuring the motion of an element comprising an element the motion of which is to be measured, a contact member adapted to engage said element, a double immediately responsive inertialess relay, an actuating circuit for said relay including said element and said member, a pair of unidirectional motors in opposed spaced relationship, said motors being so connected to said relay that either one' or the other receives power through the relay, a differential system connected to said motors and so constructed and arr'anged that `it is motionless when both motors operate at the same speed but rotates if either motor operates at a higher velocity than the other, and means operatively connecting said contact member to said differential system, whereby the contact member is positioned by movement of the system.

2. In a system for telemetering variations in the position of an element, a position gauge comprising a contact member adapted to contact the element the position of which is to be measured, a relay means, an actuating circuit for said relay means including said member and so constructed and arranged as to be closed only when the contact member is in contact with said element, a pair of unidirectional motors in opposed spaced relationship, said motors being so connected to said relay means that one of said motors receives power through ,the relay means when the actuating circuit is closed and the other motor receives power when the actuating circuit is open, a reversible element, differential gearing connecting said reversible element to said motors and so constructed and arranged that the said element is motionless when both motors are operated at the same speed but moves if either motor operates at a higher Velocity than the other, means operatively connecting said contact member to said reversible element, whereby the contact member is positioned by movement of the reversible element, and means adapted to connect said gearing to an electric transmitter.

3. A liquid level gauge comprising a float adapted to float on the liquid the level of which is to be measured, a contact member adapted to engage said float, a double immediately responsive ber, a. pair of unidirectional motors in opposed spaced relationship, said motors being so connected to said relay that one of said motors receives power when the actuator circuit is closed and the other receives power when the actuator circuit is open, a diiferential gear frame mounted for rotation about the shafts of said motors, a driving gear on the rotor of each of said motors, a driven gear journaled in said frame and meshing with both of said drlving gears, means operatively connecting said contact member to said frame, whereby the contact member is positioned by movement of the frame, said frame being adapted to be connected to, and to position by its movement, an electric transmitting member.

4. In a device for telemetering variations in a liquid level a liquid level gauge comprising a contact member adapted to engage the liquid whose surface is to be measured, a double immediately responsive inertialess relay, an actuating circuit for said relay including the liquid whose surface is to be measured and said member, a pair of unidirectional motors in opposed spaced relationship, said motors being so connected to said relay that one of said motors receives power when said actuator circuit is closed and the other of said motors receives power when the actuator circuit is open, a differential gear frame mounted for rotation about the shafts of said motors, a driving gear on the, rotor of each of said motors, a driven gear journaled in said frame and meshing with both of said driving gears, and means'operatively connecting said contact member to said frame,

whereby the contact member is positioned by movement of the frame.

5. A liquid level measuring device comprising a contact member, an actuating circuit including said contact member and the liquid the level of which is to be measured, two immediately responsive inertialess relays, one of which closes one power circuit When the actuating circuit is closed and the other of which closes another power circuit When the actuating circuit is open, a pair of unidirectional motors in opposed spaced relationship, one of said motors being in one of said power circuits and the other motor in the other power circuit, a differential gear frame rotatably mounted with respect to said motors, driving gears journaled in said frame and connected to each of said motors, a driven gear journaled in said frame and meshing with each of said drlving gears, means operatively connecting said contact member to said frame whereby the contact member is positioned by movement of the frame, said frame being adapted to be connected to a metering member in man'ner to position such member by its movement.

SAMUEL L. ADELSON.

` REFERENCES CITED 'The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,350,705 Clarke Aug. 24, 1920 1,664,265' Rieber Mar. 27, 1928 1,916,73'7 Midworth July 4, 1933 2,116,593 Bouvier May 10, 1938 2,422,313 Razek June 17, 1947 2,445,200 Wolfe July 13, v1948 A Certificate of4 Correction Patent Ne. 2,4%,3768 a Febnmry 7, 1950 SAMUEL L. ADELSON It is hereby eertified that errors appear in the printed speeification of the above numbered patent requirng correction as follows:

Column 1, line 40, for the word "detail" read deta'ilez l; column 7, line 62, for I "which" read with; line 67, for uboats read fl0at8;

and that the said Letters Patent should be read with these corrections therein that the same may eonform to the record of the case in the Patent Ofice.

Signed and sealed this 6th day of June, D. 1950.

THOMAS F. MURPHY,

Assistant oznmaoner of Patonta. 

